Grinding of cement clinker



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H. L. KENNEDY ET AL GRINDING OF CEMENT CLINKER Filed Nov. 9, 1935 0 0 0E M WM n 8 AE WM 5 0 N cc ML 44 NA 5 00 MM .W MM w 3 v MM M Z W Z 6EOIUUSS NLL L00 M xnuummlw NMDPNEMM: $32 BFPsL cw 2 3456 //N l 7 any 986 2 I I I I Reva/afions of Ball Mill Inventors 0 Henry L. KennedyCOMPOSI l lUNS,

Patented Dec. 27, 1938 UNITED STATES Examiner PATENT [OFFICE GRDIDING OFCEMENT CLINKER Henry L. Kennedy, Arlington, and Jacob G. Mark,Cambridge, Mass, assignors to Dewey and Almy Chemical Company, NorthCambridge, Mass, a corporation of Massachusetts Application November 9,1935, Serial No. 49,064

2 Claims.

This invention relates to the grinding of cement clinker.

When dry materials are ground in a ball mill, the reduction in particlesize usually progresses as a function of mill revolutions until a pointis reached known as the limit of free grind where the curve isdiscontinuous." Thereaftert'al'though the mill may be run for hundredsor perhaps thousands of revolutions, the particle size is not greatlyreduced.

The objects of this invention are to increase still further the limit offree grind; to keep the grinding media clean and uncaked formTcTngertiiire thah" measurements-pawns; to increase the output ofgrinding mills; and to prevent aggregations from occurring in the millor in the passages leading to the air separators to the end that onlyunground particles are returned. Other objects are to increase theeflicienc tain recommended cement addition agents by distributing themin a completely un anner throughout the whole mass of cement and toprovide means by which extremely small quantities of such agents may beuniformly distributed throughout the whole mill. Other objects willbecome apparent from the specification.

The limit of free grind effect has been explained by several theories,the most common, and the one usually adhered to by the operators of themills themselves, is that the balls or grinding media are coated withthe pulverized substance; that the blow is cushioned by the coating and,consequently, no further grinding can take place. Indeed, thisexplanation appears to be true, for if the mill is opened the grindingmedia almost invariably are found to be coated with a very considerablelayer of particles. But this theory by no means entirely explains theeffect for, when certain substances are added to the mill, the particlesize drops below the limit of free grin although the grinding media maybe just as thoroughly coated as before.

If the grinding of cement be taken by way of example, it will be foundthat under standard grinding practice, a very. considerable proportionof the output of the mill is run back into the mill as oversize rejectsfrom the air separators. Microscopical examination of these rejectsshows that there are two components therein; first, small singleparticles of cement clinker as yet not sufficiently ground, and; second,dense aggregated lumps of clinker, the individual particles of whichhave been ground to acceptable size.

For a number of years )eeLtallow, rgsin and oleic acid have been used toincrease the production of mills. When used, we have noted that therejects from the air separators contain fewer aggregations of particles,which means, to our minds, that tallow or oleic acid in some mannerprevents a certain proportion of aggregates from forming. We have found,in addition, that when substances such as are disclosed by Tucker in U.S. application Serial No. 643,740 filed November 21, 1932 or theHydroxy-alkyl amines as disclosed by Tucker et al. iiY'U'I'ST Serial No.756,- 082 filed December 5, 1934 orfiflll n compounds as disclosed byMark in U. S. application Serial No. 32,906, filed July 24, 1935, areadded to the clinker during the process of grinding, much lessaggregated material exists in the rejects from the air separator andthat the limit of free grind is very materially raised.

The lignin compounds are: li n sul honates, sodium lignate, the sodiumsalt 0% the condensation product of ligmn and glycerol monochlor- Hydrm,the sodium salt of the condensation product of ligmn an e y ene g ycochlorolignin,

plifiiofderivatfires of l gnin. I

e prepara ion 0 ca cium lignin sulphonates is described in the Howar paen s, eis'sue 0. 18,268, No. 1,856,558, and No. 1,958,624.

The preparation of glycol lignins is described by Brauns and Hibbert inthe Journal of the American Chemical Society, volume 55, page 4720(1933).

The preparation of phenol lignins is described by Fuchs in the J ourna oe American Chemical Society, volume 58, page 673 (1936).

Additional information, particularly concerning the preparation of cocts of 1i in is found in chapter 3 of The Chemistry of Cellulose andWood, by Schorger, published by the International Chemical Series in1926.

By following the methods set forth in this chemical literature, theproducts listed above may be produced.

These various substances are added to Portland cement to achieve certaineffects. A few examples follow:--the substances disclosed in the Tuckerapplication (sole) increase plasticity and workability of the mix. Thosedisclosed in the application of Tucker et al. materially increase thestrength of the hardened concrete.

Speaking generally, these substances have been added to the cement ortothe gau ing water by the contractor while the cement is Being mixed onthe job, but in some cases it has been the practice to mix the dryaddition agents with the dry ground cement. When such a practice isfollowed, a master batch is prepared containing the addition a ents andsome Portland cement or gypsum as a diluent in order that the very smallquantity of the addition agent may be thoroughly distributed throughoutthe whole mass of ma- 5 terial.

In order that our invention may be better understood, we advance atheory of operation which our experimental evidence appears to bear out,but We do not desire to be bound thereby. 'With the exception of coal,which is frequently added to cement grinding mills in order to purge themill or to act as a grinding a id, most cement addition agents seem tobe substances which are very strongly adsorbed upon the surface of theindividual cement particles. When these are added to cement, the surfaceenergy requirements of the cement particles are satisfied by theadsorbed layer and no bonds exist to attract other particles. Hence,treated, dry cement does not form aggregates.

Apart from theory, we note as a fact that when water dispersions ofcement addition agents are added to cement during the grindingoperation, few aggregates are formed and the production of the millrises, first, because the air separators then pick out the individualparticles which are reduced to acceptable size, and, second, (perhapsbecause the addition agent is also adsorbed on the mill walls andgrinding media), the mill does not become caked and grinding is muchmore effective. Surprising as it may seem, water may be added to cementclinker as the clinker is being ground without in any way injuriouslyaffecting the cement or adding to the water content of the finishedproduct.

This seems to be brought about because water itself is adsorbed upon thecement particle where it remains as a surface layer and, until thesurface requirements of the cement are satisfied, no hydration of thecement takes place. Furthermore, the temperatures reached by the millare sufilcient to vaporize off the adsorbed moisture and all added wateris gradually released as the grinding progresses.

In order to give the cement its maximum opportunity to pick up and holda surface layer of the addition agent, we add a wate dispersipn giltheagent to the cement while it is being ground. The vapor pressure of ouraddition agents is quite low. They are not given off or released by thecement, but persist as surfacelayer, adsorbed substances which preventlrig y agg regates from En ijig aHd later ''ii'rt their individual'ancTficuliar effects upon the cement as it is used in concrete.

In practicing our invention, we first disperse the desired proportion ofreagent to be used in water and then feed it to the cement clinker atsome convenient point, usually as the clinker leaves the proportioningtable or between the fuller or fiergul es mill nd the finisl mil}. Itmay, however, be added at other pointssuch as to the rejects of the airseparator or to one of the ferent places, for example, one portion maybe. added to the clinker as it is being fed from the, table and anotherportion added to the air sepa as we rator rejects. In general, we prefernot to use more than one part of water to 50 parts of cement or lessthan one part of water to 1,000 parfs of cement. Conditions, however,vary from mill to mill and we do not wish to be limited as to the 75amount of water used, for sometimes we find it compartments of a ggrnpqbmill. At times we find 9 it advantageous to add the reagent at severaldlfroom ation of h droxv-alk 1 amino and Fain sglfihonate f, 'gafi than5m s of gin er a e as a 15 0 solution (this comadvantageous to usegreater or lesser quantities than those above specified.

Some cement addition agents are soluble in the water used as a "carrier,other addition agents form so-called colloidal solutions or suspensions.This may be best demonstrated by specific examples. Tucker et al. usehydroxy-alkyl amines as strength producing reagents n concre e. havTodfidifitvvfiffsd caiied true solutions, 1. e., molecular dispersions,of these substances in waterarejdddtotlie "clement clinker in the mill,grindabili t y of the clinker is increased, resulting i'rTdncr asedproduction and" decreased power consumption per unit of cement produced.The grinding media are constantly kept clean and shiny; flaking of thecement is prevented; the limit of free grind is materially raised; thetemperature gradient in the mill is greatly lowered; and the finishedproduct is more uniform. Subsequently, when the ground, finished cementis used in concrete, the strength of the concrete is increased to asomewhat higher degree than when (as recommended by Tucker) the hydroxyalkyl amiggs are added to the gauge wa er. e spersing agents mentionedin the Tucker application (sole) form colloidal solutions in water, asalso do those mentioned in the Mark application. When added to theclinker in the mill, water solutions of these act in the same manner asdo the hydroxy alkyl amines, but in addition have the further functon ofpromoting a high degree of dry dispersion of the cement particles whichresults not only in cleaner grinding media, but also in a more emcientaction of the air separators.

The effect of following our invention as set forth is much greater incommercial units than in laboratory mills. This is due to thefundamental difl'erence in the mode of operation of the two mills.Commercial grinding is a continuous process and gives poor opportunityfor perfect distribution of dry addition agents due to the rapid rate ofpassage of the cement through the mill. The grinding in a laboratoryball mill, on the other hand, is discontinuous. The clinkers and agentare sealed in the mill until ground to proper size, thus much betterdistribution of dry material is effected. The more perfect distribution,however, due to following our invention, is shown even in laboratorymills by the increased grindability of the charge. Using a 20 meshcrushed clinker and an 8 to 1 steel ball charge in a steel mill thefollowing surface areas, as measured on a Klein turbidimeter checkedagainst a Bureau of Standards sample, were obtained after 2500revolutions of the mill.

Surface areas, squarecentime ters per gram Blank With agent Li ninsulhonat 1 part to 2,000 parts of a 00 as a 136% solution 1745 1920 rox'-a k l amine 1 art to 7,000 parts of I asa A solution 1880 1935 maniorms theh o u u I The drawing illustrates graphically a set ofdirectly comparable grinds. The clinker used was manufactured inPennsylvania from local materials. Each grind was made upon the sameclinker in the same mill at the same speed of rotation.

watotwOSmONS, Y comma on PLASTlC The weight of the clinker and theweight of the balls were the same in each instance.

The best combination of grinding agents (number 6) increased the surfacearea of the cement 460 square centimeters per gram of cement above theblank reference grind made according to the usual practice.

It should be understood that such a set of curves is illustrative only.On some clinkers the efiect is greater, on others it is less than ishere illustrated and each mill grinds in a somewhat different manner.

But, whatever the source of the clinker, Eastern, Central, Southwesternor Pacific, there is always a material increase in the output of themill when our invention is followed and much less aggregated material isreturned by the air separators.

In previous practice serious mechanical diificulties were encounteredwhen cement addition agents were added to the clinker because theseagents are utilized in extremely small amounts usually from .03 to .1 of1%. Consequently, the proportioning and feeding of such exceedinglysmall quantities into the mill has been a major problem. By using adilute dispersion of the agent a considerable volume exists which makesit practical to use many of the available types of liquid proportioningpumps to feed continuously the correct amount of agent to the mill, andsince the feed may be continuous and not intermittent, distribution ofthe addition agent over the cement Examiner particles is very muchbetter than any distribution which prior practice permits.

We believe ourselves to be the first to discover that cement additionagents, used for producing profound physical changes in the wet mix orfor accelerating the high early strength, are made even more effectivewhen ground with the cement clinker and, also, that these materials actas grinding aids, keep themills clean, and materially increase thelifiiit'of free grind. We have further discovered that, when thegrinding agent is composed of the materials given in our preferredexample, laitance after pouring the concrete is greatly reduced and thecement, technically, is non-bleeding.

Our discovery of the astonishing effectiveness of such cement additionagents as aids in grinding makes it now unnecessary to add deleterioussubstances such as rosin, tallow and coal to maintain the grinding rateof the mills.

What we claim therefore is:

l. The process of grinding cement which includes the step of adding awater dispersion of a lignin compound to the cement clinker in an amountinsuflicient to cause the substantial hydration of the resulting cementand thereafter grinding the clinker.

2. A process in accordance with claim 1 in which the lignin compound isthe hydroxy-alkyl amine salt of lignin sulphonic acid.

HENRY L. KENNEDY. JACOB G. MARK.

